When configuring delegation for room resources, you can use the Exchange Admin Center or run PowerShell commands to perform a batch update.
[Through Windows PowerShell]
$delegate = "admin@yourdomain.com"
Get-Mailbox -RecipientTypeDetails RoomMailbox -ResultSize Unlimited | ForEach-Object {
Add-MailboxPermission -Identity $_.PrimarySmtpAddress -User $delegate -AccessRights FullAccess -InheritanceType All -AutoMapping:$false}