Knot tips?

Hello! I have been working on and loving one of those custom image fishing line string art kits. I am a total knot novice and really struggle when I reach a point where I want to tie off.

I’ve been using the String Art Co knot from their YouTube videos but it is often pretty difficult to get it right with the fishing wire that has less friction/when my hands are fatigued.

How do y’all handle this? Any gadgets that are helpful?