It sounds like you want to user to choose to see either the AVG, TOTAL or NUMBER on the bar chart. If so you need to make use of a parameter and a few calculated fields. Firstly create calculated fields for the 3 options you want the user to be able to see in your bar chart.
Next create a parameter giving the 3 options the user is able to select.
Using the value returned by the parameter, the next step is to create a calculated field which selects the correct display measure based off the parameter. For example:
WHEN 'Avg' THEN [AVG_Field]
WHEN 'Total' THEN [TOTAL_Field]
Drag this calc into the rows shelf of your worksheet and it should work.
I have written how to do something similar in the past in more detail which could assist you if you're unsure about any of the above. It's an article on how to display user selected measures, which sounds like exactly what you're trying to do.
Hope that helps.