PR of Last surviving trustee cannot be found

I have been asked my a charitable trust to assist with the legal ownership of property of one on it’s Branchs.

The Branch was unincorporated in the 1980s at time the trustees were appointed the hold legal title for charity purposes (an unincorporated charity has no separate legal identity and cannot hold land in its own name). As it is now incorporated the Branch can now hold title in its own right.

Strictly speaking, as I understand, the Branch has no legal interest in the property just a beneficial one.

Where a sole surviving trustee dies, any estate or interest held by that trustee vests in the trustee’s executor. My understanding was that need to establish who the last surviving trustee is then get in touch with their executor (which might be the tricky part). Their executor would then execute the Deed of Appointment appointing the Branch as trustee for the lease. Due to the time that has elapsed, the PRs of the last surviving trustee cant be found.

What is the way round this? Does it require an application to the Court?