How to merge the login in the personal account on php and in the dle account?

Question

DLE

There is a DLE, where a .tpl template is built into the static page, which includes a page with a personal account, which is written separately from a separate database (page with a personal account - login.php ). I want to make it so that when entering login.php , it also enters the DLE account. Where do I need to start digging, what should I start from in order to do this? Thanks for your kind advice.