One thing you can do is offer them small boulders or a shallow pit of gravel. This may seem dangerous for a drilbur, but this is actually necessary for the maintenance of drilbur’s claws. Gravel pits give them something to dig into that will “refill” itself eventually, and boulders offer larger surface areas to scrape. (It’s extremely difficult to maintain a drilbur’s claws otherwise, although with patience, a human may be able to use a claw file on them. Drilbur generally don’t sit still long enough for this process, however.)
Planting logs or stumps (if one of your neighbors is looking to remove a stump from their yard) may provide obstacles for a drilbur to play with, especially if either of them have thick roots. They can also encourage insect breeding and provide something natural for a drilbur to snack on. Do not plant actual trees, however. Drilbur activity can damage the tree’s roots, which means planting trees in your drilbur’s “territory” may endanger them. The same can be said for gardens, incidentally (although you can use any area of your yard that your drilbur has grown tired of to garden).
Otherwise, simply giving your drilbur plenty of space (such as your entire yard) will be sufficient enough. Your drilbur will create tunnels and occupy themselves on their own, basically.
Other than that, drilbur eat insects, worms, and nuts when not on kibble, and they will often find sources of these on their own. However, it’s still recommended that you feed them regularly, especially during the winter, as those three food sources may not be plentiful enough to support your drilbur exclusively. Give them clean water for drinking as well, but keep in mind that as ground-types, they should never be bathed or placed in a wet environment. (They’ll self-groom, but you can provide them a sand bath as well if you can afford one large enough for them.)
They’re also mainly outdoor pokémon, so while you should bring them inside during the winter or during heavy rains, they can actually survive well enough by being left outside. Additionally, some trainers worry about whether or not their drilbur will wander or create tunnel systems that travel too far away from home, and quite frankly, these are valid worries. Some drilbur do dig burrows that lead far, far from home, but others prefer staying close and digging downward. To curb the potential of your drilbur digging too far from home, offer your drilbur treats and a warm, dry place for inclement weather. This will encourage it to come back or keep its tunnels close to you.
Good luck, anonymous!