Accidentally changed dev seat to full seat

I have a professional plan with two seats. One full seat and one dev seat. I accidentally changed the dev seat to full seat by granting editing access to someone on dev seat. And now my entire plan has changed and I have two full seats that I don’t need and I can’t turn it back to dev seat without costing me more. And now I have a billing for 43 per month. This account is for the company and I don’t want any additional costs for the company. Please help me it’s so urgent and if I don’t solve this or pay the new bill, I will lose my access to the file.