I have table1 and table2

In table1 I have

stID (PK)
Name
dateOfBirth
schoolId

in table2 I have

serviceId(PK)
serviceType
stId

the two tables are related using the stID key

stID is numerical field starting 100 and I have about 200 records in the first table
Now, Single data entry for one person is working fine using a single form
I just type stID and the service type value.
Now what I want is that once I enter the service value for one person let say stID 145 then I also want the service type value to enter for the rest 199 individuals automatically
Is it possible ???
Thanks in advance