PAIRED bt mouse with another computer - trying to re-PAIR it back on first computer

Paired my working Plugable bt-mouse3 to my son’s computer for Christmas. He used it for 24 hours. I powered down his computer and attempted to re-PAIR the mouse to my computer again. Tried depressing the CONNECT button monentairly and for 8 seconds. Still Won’t PAIR. Removed the batteries and re-installed the batteries and tried above steps again. Still won’t PAIR. ANY SUGGESTIONS?