Help Connecting One to Many Relationships

I’ve committed a classic novice mistake in making a very an unsustainable, time consuming table with many columns. I have three tables

GYM SESSIONS (my new table to link to reference to ACTIVITIES)

In the activities table, a user may select 5 activity choices: RIDE, INDOOR BIKE TRAINER, RUN, YOGA, and GYM SESSION. With GYM SESSION specifically, there is a ONE TO MANY relationship as you may have many different workouts related to the one the activity.

My mistake: in my app, I have created up to 20 different Entries for GYM SESSION specifically and made it so that it’s VALID IF only GYM SESSION is selected. This has resulted in a very time consuming effort in setting the parameters of 60 different columns (1 entry is composed of WORKOUT, WEIGHT, REPS, SETS).

I know there is a way to create a separate table so that when a GYM SESSION is selected, the table can be referenced as opposed to what I did and create all these extra columns in the Activities table.

Knowing this, I created the table GYM SESSION which includes GYMSESSION ID (KEY), WORKOUT, WEIGHT, REPS, AND SETS.

The workouts (eg. Squats, Bench Press, etc) is defined in my DATA_VALIDATIONS table which includes a lists to references.

How can I connect the GYM SESSIONS table with the ACTIVITY table so that it’s called up anytime GYM SESSION is selected?
Here is a link to my working app.

Use REF_ROWS("[Table name]","[Reference]"). That’s how you connect one table or sheet from another.

Still not sure how I can connect the GYM SESSIONS form with the ACTIVITY FORM based on GYM SESSION selected?

Is there an ACTIVITY column in the GYM SESSIONS with type REF pointing to the ACTIVITY table?