Unfortunately, GoSimpleTax cannot be used to complete or submit a Trust and Estate Tax Return (SA900).
If you require software for filing an SA900 return, HMRC provides a list of approved commercial software suppliers here:
Please note that GoSimpleTax does support the Trust Pages (SA107) within an individual Self Assessment tax return (SA100), allowing you to declare personal trust income where applicable.
You can find further information and guidance on completing SA107 forms in HMRC's Trusts etc. Notes: