There are two ways transactions from Splitwise interact with the All Transactions Table.
The Splitwise transaction corresponds to a transaction from one of my accounts (I paid for a group expense) and friends are reimbursing me for it. The amount in the transaction on my account should only reflect my share of it and not the group cost. Search for the transaction from my accounts and add it in the Related Transaction column. This will automatically deduct the amount from my account transaction with the Splitwise transaction so what remains is just my share of the group expense.
The Splitwise transaction corresponds to a transaction not already existing in one of my accounts and needs to be added to the All Transaction Table. Use the “Add to Transaction Table” to copy over the row into the All Transactions Table.