How can I separate the glass from the lcd screen?

Actually, it is possible to do a front glass replacement, but a professional job requires things like a vacuum table with wire guides to separate the screen from the glass, along with a vacuum chamber to remove the air bubbles from the OCA and a UV chamber to cure the glue.

For us DIY'ers, there is a company making kits designed to allow you to do that job yourself. I actually attempted it myself, but ultimately I ended up damaging the OLED while trying to separate it. It was a good learning experience, and I suspect with some practice it might work sufficiently for home use, although I don't know if the end result will actually look like a new screen.

Anyway, I'd say your best bet is to try one of those kits; you may have better luck than I did. Here's a link to what looks like the right one for your phone; be sure to confirm that for yourself before purchase.

Patent Pending DIY Samsung Galaxy Note 10~20 Ultra Front Screen Glass Repair Kits – ExpertCellDIY

In my case the replacement screen was so expensive that I figured it was worth a try; I did end up doing a full screen replacement because I didn't get the initial separation done correctly and damaged a chip out of the OLED. But hey, for $30 USD I felt it was worthwhile.

Good luck and let us know if it works out for you; it would be great if you took lots of pictures as you work and use those to create a guide to that repair here on iFixit!