If you mean that when you check out of eBay and select PayPal, you are not able to choose a specific payment method in your PayPal wallet but one is selected for you, in that case go to your eBay Payments page in your eBay account and delete the entry for PayPal that appears there.
As long as you have another payment method still linked, deleting the PayPal entry should not affect anything else, but you should be able to go to your PayPal wallet again when checking out and selecting PayPal.
