Getting one of Two iMacs ready to Sell

I have two iMac's both running macOS Monterey. One for home, and one for the office. Now that I work solely from home, I have an extra system.

Today I learned through reading Apply Support that I cannot connect the two using Thunderbolt cabling. The option now is to erase everything and prepare for it to be sold.

Can you direct me in to proper procedure to erase one of them. When I sale, I am hoping that it has original settings when I bought in 2018. Please advise procedure.