You have a couple options:

1. For a fee, Coradine, can go through all your old logbooks and manually input. Data entry essentially. Would be very cost prohibitive though and not worth it in my opinion.

2. Sit down over a many month/year period and do it yourself. No cost but ends with same result as above.

3. Do what I did. I was in the same boat as you. Input one single entry called "balance forward". 15,000 hours. Break it down with single/multi/jet/instrument and whatever. Go from there. Much easier and done in a couple of minutes.

Good luck.