Hello there, @infojmupholstery.
I'm here to provide details about HMRC's Self Assessment. This way, you'll be able to know when is the best time to fill it in to comply with your government's deadline.
You're required to register for Self Assessment on or before 5 October 2019.
You should file your tax return to the HMRC by the deadline. In case you have clarifications about the registration and its deadline, I'd recommend consulting with the HMRC directly. They can assist you in registering an account and guide you with the things you need to perform to complete the process.
To know more about the HMRC's Self Assessment tax returns, you can refer to this article: Self Assessment. Its contents include the self assessment overview, deadlines, and penalties to name a few.
Please let me know if you have other concerns. I'm just around to help.
