In my phone ghost touching is automatically on

The phenomenon known as ghost touch happens when the delicate connections between the flex cable and the glass the digitizer circuitry is printed on get damaged or disrupted. That allows electrical noise onto the signal lines, which the processor interprets as touch inputs. Unfortunately, that kind of damage isn't repairable and the only fix is to replace the screen.

While iFixit doesn't have a guide to that repair for you, their teardown video would suffice if you wanted to replace the entire screen+frame assembly. This is actually the recommended way to replace the screen, as the new display comes already mounted on the midframe. If you're not familiar with phone repairs this is the better way to do it, as there is less that can go wrong. Basically, you open up the phone, remove all of the interior components, and transfer them to a new screen+frame assembly, exactly as shown in this video.

Xiaomi Redmi 7A Teardown - iFixit

The other way to do it is to purchase the screen alone without the frame. This process requires less removal of parts, but is somewhat harder due to the need to clean the old adhesive from the frame and glue the new screen on. This kind of repair requires a completely different set of instructions; luckily the Spanish site Nadie Me Llama Gallina has just what you need.

Manuales / Xiaomi Redmi 7A / screen - Nadie Me Llama Gallina

As far as buying parts, you can purchase a new screen either with or without the frame. The frame only adds a few dollars to the cost, but the advantage is in being attached at the manufacturer, so it will be as water resistant as possible. If you choose to buy a screen without the frame, that savings could easily be offset by the need to buy glue to resecure the screen; generally people use something like B-7000.