Printer Help for now

my hp2800e printer stopped connecting to wifi about 2 weeks ago.  Is there a link that will explain how to split it from 5g to 2.4?  I tried but I am 73 and I need explicit instructions.  I can't use the app because I have the iPhone 8 and  it will not upgrade.  I tried calling numerous times for help.  some of the online instructions are for windows; I have a Mac so it's confusing and I need my printer to work asap.  Never had this issue until after the internet went down recently and I was notified it was for upgrading.  That took out my security system; my furnace, my ring, and was told I could not get a refund.  Since that date, my printer will not get a signal.  HELP!