eGFR of 39 with only one kidney - cause for concern?

I’m 4 months post-complete nephrectomy with an eGFR of 39. Receiving Keytruda infusions every 6 weeks for Stage 3 clear cell renal cell carcinoma in hopes of preventing spread or recurrence. Nephrologist doesn’t seem too concerned about the eGFR rate being 39 or the creatinine level staying at 1.9, but I know those are NOT ideal numbers. Any cause for concern, and also anything I can do to try to improve those numbers?