Converting indirect recursion to direct one
$S\to A$

$A\to aA'|EP$

$B\to CDB'$

$B'\to AB'|EP$

$C\to bC|EP$

$D\to aD'|bC'DB'bD'$

$D'\to B'bD'|EP$

There is a standard algorithm to remove indirect left recursion check here https://en.wikipedia.org/wiki/Left_recursion#Indirect_left_recursion