How to modify exported variable and use that modified variable again into running script?

Question

I am running one shell script inside another shell script and want to modify exported variable and use that modified variable again into running script.

#! /bin/bash
export a=0
echo $a
./deploy.sh  #calling deploy.sh script
echo $a      #To see modified variable
echo $b

deploy.sh script is

#! /bin/bash
a=1
export b=a