Hi Neil55,
I would advise that if you are already in possession of a Self-Assessment record to submit a Tax Return for any year that criteria has been met in order to disclose the short-term letting property income, using the appropriate SA105 Property supplementary page for the year in question.
You may still submit any Tax Returns from the 2019/2020 tax year onwards online here:
Self Assessment tax returns
with any prior year only submittable as a paper version here:
Self Assessment forms and helpsheets
Thank you.