Hi The_Wax_Company,

This is NOT Amazon Support but a forum of other Sellers.

To downgrade your Professional selling plan and change to the Individual selling plan then you need to go to settings (cog wheel, top right) - Account info / Account management / Downgrade Account / Sell on Amazon (click on pull-down) / and click on Individual Account for the Markets you want. Then Save.

I have read that the next step is to approach Seller Support for the refund which they should do if you have not used the Pro Plan benefits

I have never done this and am extrapolating from other Sellers' advice (thank you @Seller_ZVAz3d5lZuGid)

All Best

Brian