how can i do it

Easy.
First, it is better to create a new VIEW for this, rather than changing one of the built-in VIEWs.

% Work Remaining = 100 - % Work Complete

Use a spare Number field/column, such as Number1, to do the calculation (Tools, Customise, Fields).

Number1 = 100-[% Work Complete]

Then use a formula in a spare Text field/column (Text1, Text2) to include the "%" sign and some title text for the display:

Text1 = [% Work Complete] & " % WORK COMPLETE"
Text2 = [Number1] & " % WORK REMAINING"

For convenience, rename Text1 and Text2

Text1: PERCENT WORK COMPLETE
Text2: PERCENT WORK REMAINING

Then use Format, Bar Styles, Text (tab) to show Text1 and Text2 on the ends of the bars.