Hey Alxa, welcome
Two essential commands for controlling a demo are /gamespeed and /seekdemo, the first one lets you speed up and slow down time, the second one lets you skip to a specific time ahead.
gamespeed is very intuitive, but seekdemo can be confusing at first, for example /seekdemo 9:00 will jump to 1:00, and /seekdemo -9:00 (or /seekdemo 1:00) will jump to 9:00, both positive and negative numbers will skip forward, the only way to "rewind" is to reload the demo before the seekdemo (eg /demo demoname; seekdemo 5:00), but you don't have to worry about any of that if you use the Pseudo Demo Editor addon (
https://github.com/SalatielSauer/Sauer-Demo-Editor/) :P
I'm not sure about the avatar requirements, but you can try asking on Sauerworld discord channel #support:
https://discord.gg/j3kyxtj