In order for you as a user to be able to split your expense, the Split expense function must first be activated for the organization by the administrator.
If you are missing the option to split an expense, you need to contact your organization internally.
You also need to add a receipt image to the expense in order to be able to split it.

Once the function is activated and ready, you as a user will see the option Split receipt in the expense. The expense can be split as many times as you like.
 

To split your expense, open your expense and scroll down to Split receipt.

Fill in the information on each row under Split. If you want to split the expense further, click the button at the bottom, otherwise select Save when you are done.

The Expense splits field shows all your split expenses. If you want to make any changes to your split expense, click on the three dots on the right-hand side of the page and select Edit split. Here, you can also remove your split.

Click Save when you're done.