My hair is blonde and very porous. I changed hair color to a darker blonde and it had a blue base in it. It did great on the roots but where my hair was already colored blonde it turned it blue. What do I do to get this out. Should I use a toner with an olive base? Thanks in advance for any help.

Applying a toner on blue hair will not make it blonde again. You will need to stripped the color from your hair first and then apply a toner.