Yes, you can use your own funds and/or money made available to you by third-parties (e.g. relative).
If you look here on the UKVI website:
https://www.gov.uk/tier-1-entrepreneur/ ... ment-funds
Under "Tier 1 Graduate Entrepreneur", it states that if your last leave was Tier 1 Graduate Entrepreneur, then "your funds can come from any source".
In the policy guidance, on Page 9, it states:
Tier 1 Graduate Entrepreneur
"You have access to at least £50,000 which is available to
you or your business and they are:
1. applying for leave to remain
2. have, or were last granted, leave as a Tier 1
(Graduate Entrepreneur)
I also had the Tier Graduate Entrepreneur Visa and switched to T1E using funds from a relative.