Whenever a database is posted my first reaction is to look at your tables and not even register what you are posting about. I do this because if the tables are not structured properly there's no point trying to fix whatever your issue is because it would be applying a fix to a system that has bigger problems than what was posted about.
This is true in your case. I suggest you put away whatever this issue is and learn about normalization (
https://en.wikipedia.org/wiki/Database_normalization). Your tables are not set up correctly and whatever issues you have are probably just a symptom of this much larger issue.
Although I have very little knowledge of the what this database is to do, or how you've set up the tables I see common major errors in what you have done:
1. Not using autonumber primary keys. First, no table you posted has a primary key defined--this is important, ensuring uniqueness in a relational database (where you link tables together in queries) is imperative, primary keys accomplish this. You did use an autonumber for Users.UserID, but you did not make it the primary key.
2. Data suffixed/prefixed to field names. When you have fields like [MonACYes], [MonACNo], [TuesACYes], [TuesACNo], [WedACYes], [WedACNo] you have done both these things. Mon/Tue/Wed, etc is data and should not be in a field name, but in a field as a value; likewise Yes/No are values that should be stored in a field. Those 14 fields (7 days * 2 Yes/No) should become 3 fields in a new table-->1 field to hold a foreign key that ties back to WeeklyChallenges table (foreign key/primary key are integral concepts to database, learn them:
https://www.w3schools.com/sql/sql_foreignkey.asp), 1 field to hold the day of the week and 1 field to hold the Yes/No. Then in that new table you have 7 rows for a week of data, not 1 field per day of the week.
3. Duplicated data. I am not sure you are doing this, but you have tons of fields in Weekly_StartTime_Challenges that are also in Weekly_Challenges. Is this the same data in both tables? It shouldn't be. Using the concept of primary/foriegn keys you only store data in one table and then link the tables by those keys when you need it all together.
4. Calculated data. This data does not belong in a table. I see numerous calculated fields in Weekly_StartTime_Challenges and they simply should not be there. Instead they should be in a query. Access did a bad thing allowing those types of fields into their tables and should not have done it.
So, I would put aside whatever issue you posted about and start about fixing the tables of your database by following the rules of normalization.