my wifi seems to not cover my full apartment

superstar

I have an old bell modem, can i connect and create a guest network for guests? or can I get a 2nd fizz modem using my same plan?

Ihssan

You need something like this

https://www.amazon.ca/s?k=wifi+extender&ref=nb_sb_noss

Or stop using fizz wifi and use something like this

https://www.amazon.ca/s?k=mesh+wifi&sprefix=mesh&ref=nb_sb_ss_ts-doa-p_1_4

Bell mode/router dont have the options you need and fizz wont give/sell you a second modem (one per account/adress)

The guest option you talking about will only work if you plug it with a long ethernet cable to fizz and place it where it's signal can reach the other side of the appartment.