CommanderOne: Clear the servers history
I got my answer from the CommanderOne support:

To clear the history of the list, use the following command in Terminal (Ctrl+O):
defaults delete com.eltima.cmd1 TCXWindow.connect2addresses
Please, note that settings ID (com.eltima.cmd1) varies based on Commander One version, that you have installed:
Website: com.eltima.cmd1
AppStore free: com.eltima.cmd1.mas
AppStore PRO: com.eltima.cmd1.pro.mas
SetApp: com.eltima.cmd1-setapp