Safety Knights

It depends on the configuration of your racks and which tier they're working from, but in the past, I've had them tie off to the racking using an anchor/cross-arm strap around the column.

You would need to evaluate the structural integrity of the rack, though. If it's damaged at the tie-off location, then I would not use it.

Depending on your location, some states also require an RPE to approve "certified" anchorages.

One of our sponsors, Access Safety Specialists may have a solution

We have folks go up in Orderpickers, on fall protection (harness and SRL) with a platform. Internally we use flat top pallets (standard wood pallet with plywood top) to pick product. We discourage entering the racks so we give them tools like long handled rakes to fix what they need.