How can I build a weight and balance for a six place aircraft? Cessna 210L?
First, make sure you have built an Aircraft Profile for your plane: Menu > Setup > Aircraft, then either Edit (if you already have a profile, you can review and make updates if necessary) or Create New Profile. If creating a new profile, choose "Manual Entry", enter your tail number, then search "210" for pre-built profiles to choose from. There are several Cessna 210 variants, and you may need to look at a couple to decide which one is the closest match, then you'll probably have some tweaks to make so it is a solid match for your specific plane.
Once you have a profile in place, you can add W&B info to it. Scroll to the bottom of your aircraft profile and tap on the Weight/Balance field. Unfortunately, there is no C210 in the pre-built "Aircraft Database" there, so you'll need to start from a "Generic Airplane". There's also not a 6-seater in that list, but pick the 4-seater and you can modify it from there.
Under STATIONS, click +ADD > Seat(s), change the name to "Middle Seats" and click Done, then fill in the Arm, Quantity (2), and Max Weight (if desired), then click Done. If desired, tap the RE-ORDER button and re-order the stations as you prefer to see them.
At this point, you have a template that you can customize for your plane. Add (using the +ADD buttons) or modify/delete (by tapping on the station's box) any other stations appropriate to your aircraft. Adjust the Empty Weight, Empty CG, station arms, individual station weight limits, and especially your CG envelope limits to match your plane. When finished, Save/Close the form.
After you have your W&B template defined, then you can fill in the details for a specific flight and see the calculation results via Flight Plan > Wt/Bal.