Hi, help with another look up field value problem

Hi, help with another look up field value problem

HI there, thank you for your hard work!!

How can I export a value from Field1 FormA to another Field1 FormB while still staying in screen at FromA?

Field1FormA needs to hold same value as Field1 FromB while still on same screen at FromA

I have two Forms

Reserve_Ride
With fields   Number of Seats Total (which is set to 8 as set value)
                  Number of Riders (Customer enters the number of rides to purchase)
                  Current Seats Available (has a formula that has 8- number_of_riders)
                  Choose Date and Time (Lookup for Add_New_Ticket formula one)
                 

Add_New_Ticket
                   Formula 1 ( puts together type of ride, day time ect)
                   Current Number of seats (current_seats)

Now here is my question?? how to code ??
automatically update the value in field/view Add_New_Ticket.current_seats

with the value at Reserve_Ride.Current Seats Available as soon as the customer enters the value in (Number of Riders)

Without the customer having to actually go to form Add_New_Ticket and input value
Thanks in advance!!

The goal of this is that when making a reservation, the customer selects a value from Choose Date and Time (formula 1 (date, time, type of ride, !!!------ number of seats available!!!) and can also see the number of seats available in the formula_1 (from previous entries). This way we won't overbook =)