Locate the password reset jumper (PSWD) on the system board. Remove the jumper plug from the password jumper-pins. Power on without the jumper plug to clear the password. Wait until the desktop is loaded and then shut down the computer and replace the jumper plug in its original location. Or...
This is the Wireless Mouse I bought to go with it, works a treat. https://www.amazon.co.uk/gp/product/B06ZYJB46P/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1