andy

Agree with Minho however a good thing to check is Night Shift is off as this will change the appearance of the display.

The 6S doesnt like water and really causes problems in this model however also can be quite resilient to brief water contact due to the glue seal all around the screen. If you have not opened a 6S up before & not used to iPhone repairs I suggest you dont try, 6s has a glue seal all around the screen so you may crack the screen upon removal. Leave it to a expert but needs opening ASAP. The longer you leave it the less chance of suvival due to corrotion forming. May not be that wet inside but need checking and do not charge it. Also they are prone to blowing circuit board parts once wet which is specialist repair. Minho gave a great breakdown on what to do.

As the iPhone Guy suggests, you need known working test parts to effectively troubleshoot. Then once the problem is found you can just replace the faulty part.

What is the previous history of the phone? eg stopped working all of a sudden, been dropped, got wet etc. Are you skilled enough to unclip the screen to push on the sim holder?

What you need is a good skilled iPhone repair workshop that does microsoldering not a corner shop. They can remove the shields and inspect the logic board. Repair if required. It will need a known good screen too. As long as nooone has tried to reset the phone via itunes there is a good chance of success. If you car'nt find anyone let me know and I can take a look.

Your best bet is to look on youtube. look for something like iphone 6 oca screen refurbishment. Basically on your screen you have multi layers. The bottom layer which is the LCD/touch screen, then the polarizer on top, then the OCA on top of that, then the top peice of glass. You have removed the glass and the glue is left, known as the OCA (optically clear adhesive), you probably have left the polarizer on the LCD which is fine, leave it (its the black looking layer on the LCD). Propper screen refurbishers would replace the polarizer for 100% perfect screen, sounds like your very new so I would use the old 1.

As Rayeasom has said, check everything is seated correctly, if so then you have probably damaged the home button cable. If problem persists after checking cables & connector fit a new home button, if that fails fit a new extension cable. If you do fit a new home button you will loose the fingerprint function. As a temporary fix use assistive touch in settings which will give you a on the screen home button.

If you have tried a known working sim, flicked airplane mode on/off, resetting phone etc next step is to Go into your settings and check if you have a IMEI number, if not your baseband IC is faulty and basically not worth fixing. The IC can be changed by a specialist but needs recoding and im not aware that this can be done easily.

Wow thats a long post, sounds like you have multiple problems. firstly the history of the phone is unknown so I would go for long screw damage on the lcd metal plate anchors for the blue screen. If a long screw is put into the wrong place this basically drills intot he circuit board and cuts tracks. This is a very expert fix if at all possible. This needs sorting 1st. long screw damage will cause blue screen of death, it can be intermittant. remove the lcd connector screws and have a look inside the thread hole and see what you can see, if you see anything that looks like copper your in trouble. also leave the screws out and see how the phone works as the long screw may still be used and causing problems. Other issues cauld be pry damage when you have removed the battery or just a crap battery but without fixing or ruling out the long screw damage your wasting your time.

You need to first determine if the phone wont turn on or the screen wont turn on. Plug it into itunes and if it connects you have a lcd problem, if it says your in recovery mode you may be stuck in DFU mode, holding the power & home button for 10-15secs will reboot your phone. If the phone wont do anything you either have a bad battery or you have damaged something when you changed the screen. That little metal thing wont stop the lcd from tuning on and bending the lcd tabs wont do anything either.