I can't use the web interface because I have 2 lighttpd services

[chrislph]

You can change the Pi-hole port

How can I change the default port of pihole? (changing lighttpd.conf not working)

Don't change that file, unless you are aware and willling to deal with the consequences. Quoting directly from that file: ############################################################################### # FILE AUTOMATICALLY OVERWRITTEN BY PI-HOLE INSTALL/UPDATE PROCEDURE. # # ANY CHANGES MADE TO THIS FILE AFTER INSTALL WILL BE LOST ON THE NEXT UPDATE # # # # CHANGES SHOULD BE MADE IN A SEPARATE CON…

Or you can change the port of the other instance, but whether that is possible depends on the other application and how it handles it.