How can I stop a piece of history from being shown in "Firefox Suggestions", which was made on an unapproachable device?

I just want to stop a piece of my own history from being shown on "Firefox Suggestion", which was made with a firefox browser on my previous device and is relatively private.(I know I can do this by modifying "Search Suggestions->Show search suggestions ahead of browsing history in address bar results", but I would like to preserve the function itself). That device is permanently unapproachable, and so is that browser. I tried "Clear recent history -> Everything", but it didn't work as expected and that is still shown. I think clear all my history(not only those made on this currently used device) may help, how can I do it?