Nothing to worry,early CKD, easily manageble. if he is older than 60-65 egft 50-60 is goog.
I would start him on NOCID tablet and vit B12 with vit D3 with K2, ask your doctor about it, control his glucose intake, limit white or brown rice to once to twidays until serum creatine go low, 2.5-3 l of water per day,nothing else, no sada,no liqor no coffe or tea, for 3 mothsn, within 3 months he will be fine,
Best diet for him is canivore if you can do it, and always take serum creatine test in the evening ,before the test dont let him eat any meat items give him enough water too,