1solely engrossed in one thing
2just (one thing, no need to worry about the rest)
3simply
4by all means
5please feel free
6do not hesitate (to ask for sth)
Example
nǐ你yǒu有shén me什么huà话，zhǐ guǎn只管shuō说。
你有什么话，只管说。
Whatever words you have, just say them.