There is no need to use a warming filter.
A White Balance adjustment lets you do that.
Look on page 59 (bottom half of page) of the Instruction Manual.
The subject is White Balance Compensation.
You can bias the Auto white-balance toward the red.
If you want to use a glass filter, then make sure that the white-balance is not set on Auto. Use any other setting.
If you are outside on a sunny day, set the whitebalance to 5300k and then mount the filter. (page 59 top half of page)
In other lighting situations you can set the white-balance using the One-Touch feature and then mount the filter (page 60).
I have an Olympus DSLR E-510. My question is that if I want to use a colored filter on it, how can I prevent the Auto white-balance trying to cancel it out? If I use manual settings, how do I decide which one to muse? The question is about using warming filters like 81b.