Use this formula that creates a true date/time: REPLACE(LEFT(A1,LEN(A1)-1),11,1," "), adds 12 hours: +TIME(12,0,0) and then formats it back to the original format "yyyy-mm-dd\Thh:mm:ss.000\Z":

=TEXT(REPLACE(LEFT(A1,LEN(A1)-1),11,1," ")+TIME(12,0,0),"yyyy-mm-dd\Thh:mm:ss.000\Z")

Use this formula that:

1. Creates a true date/time: REPLACE(LEFT(A1,23),11,1," ")
2. Adds 12 hours: +TIME(12,0,0)
3. Then formats it back to the original format "yyyy-mm-dd\Thh:mm:ss.000\Z":

=TEXT(REPLACE(LEFT(A1,23),11,1," ")+TIME(12,0,0),"yyyy-mm-dd\Thh:mm:ss.000\Z")