I think you might be a bit confused about what the OP has done... OP has sent two transactions:
Transaction One, Sending to Exchange, low fee:Input A -----> Output A1 (Exchange Address)
|
|---> Output A2 (Change Address)
Transaction Two, low fee:Input A2 ------> Output B (Receive Address, different wallet)
Now, the OP is attempting to clean up these two transactions, by doing a 3rd transaction... which is a CPFP that will cover all three transactions. The formulas for this will be something like:
Total Fee required for third transaction = (Transaction One bytes + Transaction Two bytes + Transaction Three bytes) * current recommended fees
Fee rate for third transaction = Total fee required for third transaction / transaction three bytes
Given Transaction#1 was 1 inputs, 2 outputs, it should be around 226 bytes, Transaction#2 had 1 input, 1 output = 192 bytes... Transaction#3 size? difficult to say, depends on how much BTC is in Output B and can it cover the fees... if so, it could theoretically be 1 input, 1 output...
https://bitcoinfees.earn.com/ is currently estimating 500 sats/byte... so :
(226 + 192 + 192) * 500 = 610 bytes * 500 = 305,000 sats required fee... so transaction#3 should be sent with 0.00305000 BTC
total fee... or 305,000 sats / 192 bytes = 1589 sats/byte fee (0.01589 BTC/kb)