Welcome. My name is XXXXX XXXXX would be glad to assist.
You can use the 3/0 for a service. If it is THHN wiring, it is rated for 225 amps.
If it is a USE-2 or XHHW aluminum in underground cables, it is rated at 175 amps
It is just a one resident dwelling, with a 200 amp panel, was wanting to up grade to a 3/0 wire.
200 amp panel is 4/0 aluminum or 2/0 copper wire, so if it is copper now, the 3/0 carries more than the 200 amps and is certainly capable of taking care of the panel.
You are most welcome, glad to assist