Thanks for visiting the Community, @craig52.
In QuickBooks Online (QBO), the option to edit the transaction amount in the For Review tab is currently unavailable.
However, since you only want to record the business portion of the expense, you can enter it directly into the register, then manually changed the status to C (cleared) as a workaround.
For more insights about entering transactions directly in a register, check out this article: Add transactions to accounts in QuickBooks Online.
Once done, you can just exclude the bank transaction in the For Review tab. For further guidance with the process, refer to this article: Exclude a bank transaction.
Just in case, I'll add this article that tackles paying business expenses with personal funds in QBO: Pay for business expenses with personal funds.
In the meantime, I recommend visiting our Blog site. This is where we share recent happenings and future developments, such as updates to newly added features.
Reach out to me in the comment section below if you have any other questions or concerns. I'll be more than happy to help. Have a good one!