Thomas Dougherty

I am completing Self Assessment via hard copy forms because I am a non-resident landlord. I have received income from a trust. The trustees have told me that I am due a tax credit. SA107 only asks me to state my income, but I don't see an option to give the trust's UTR or otherwise indicate the tax credit. When I submit my self-assessment, how do I notify HMRC about the tax credit that I am due? Thank you for your help with this