How do you go finding your keys?
I rarely lose mine, mainly because I always put them in the same place. Have you ever asked God where they are? Of course God would have no problem finding them because He never forgets and is perfect in knowledge.
Don't you wish you could misplace your sin like you misplace your keys?
How is it we struggle to find the things we really need (keys) but can't lose sight of the things we don't want to see (our sins)?
There is a difference between forgetting and not remembering. God can't forget, He just chooses not to remember.
Hebrews 10:17 - "Their sins and lawless acts I will remember no more."
God doesn't bring it up because it has been dealt with at the cross. He actively chooses not to remember our sin once we have been cleansed by the blood of Christ. Your sins are dealt with once you surrender your life to Jesus.
You don't have to try and forget your mistakes and sins, you have to work on not remembering them!
God can't forget where you have placed your keys and He won't remember your sin, in Christ.
God is NOT absent minded!