A number of ways.
1. Delete the contents of each table, then compact the db - this will reset the autonumber to start from 1
2. For each table, copy using ctrl-c (or right click and select copy), then paste using ctrl-v (or right click and select paste). You will be prompted for the type of save - select structure only. Note you will need to save with a different name. Then you can change the name back to what it should be so it overwrites the old table. Then compact the db if required.
but probably the easiest way is
3. Create a new db, copy the tables across using the facility under external data but before copying, select options and change the option under Import Tables to Definition only
Note if you have linked tables you will need to go to the source db to undertake the above
