Entering the UK on BRP expires

I was approved for my Tier 5 mobility visa in April and my original entry date was May 21, 2019.

I had a last minute change of plans temporarily and have yet to reapply for my BRP simply due to one of the gov.agents advising me I could wait until I was closer to my new intent travel date.

I was contacting a new agent for more information where they advised me this was not the case and that I should have reapplied for my BRP 3 months from my newly intended travel date which I of course did not do because of what the previous agent advised me of.

Basically I am wondering if there is any way I can go to the UK on my Tier 5 visa in February 2020 vs. the May 21st 2019 I originally aimed for. Is there particular steps I need to take to make this possible as I really want to utilize this visa.

Thank you in advance.