https://help.gosimpletax.com/hc/en-gb/articles/206806270-How-Do-I-Transfer-My-Partner-s-Personal-Allowance-

https://help.gosimpletax.com/hc/en-gb/articles/206806270-How-Do-I-Transfer-My-Partner-s-Personal-Allowance-

Click Validate My Tax Return     Select the 'YES' radio button to indicate that your partner has made an election to transfer their personal allowance to you