I got a warning that said I have been infected, not to turn off the compute

I was on the site pdfiller, I use the site often to complete legal documents. I was going to download a manual for a motorcycle and several pop ups appeared on my screen saying I have been infected, not to turn off my computer, to call a phone number.

I right away disconnected the computer from the internet and turned off the wifi. I got on my phone and looked up the warnings and saw this is malware and a scam, as the message did say to call a phone number.

I think I need to not boot the computer until I can scan it, clean it. Not sure how to do this.

The computer is an Acer Nitro, is there a recovery mode or do I create a USB boot?

Thanks for any help.