Please explain what do i do if blood gets into the insulin pen that i use?

Hard to do: Hi. I can't imagine more than a tiny, tiny amount getting into a pen, since pens can't aspirate. I suspect the minuscule amount of blood that could diffuse up a 30 or 31 gauge pen needle is so tiny that you don't have to worry. There can be proteases in serum that can digest proteins, but I don't think you will have to worry about this.

Unusual problem: I have never actually seen this happen. There must be something defective about the pen you are using. I would discard it and use a new pen. There is no mechanism for drawing back on the pens, so it should never occur that blood goes into the pen.