Thanks, Paul.
In this case (and as long as this 10.5 ETF was the complete component of this particular ISA wrapper), rather than managing any sell down yourself, you would need to request the transfer with the new provider.
This new provider would contact InvestEngine and we would work with them to agree to pricing and timing of a transfer as well as amount to be sold down as cash. We would then initiate this sell down and you will receive confirmation of receipt from the new provider.
You need to make sure that when you make this request with any new provider, you specifically request it as in-specie to ensure the process above is triggered.
I hope this helps and if you are heading off elsewhere, we’ll be sad to see you go but wish you the best in your investing future!