Use setenforce 0 for permissive
or
setenforce 1 for enforcing
can do via property in ramdisks bootinfo using CMD_LINE=bootopt=android.boot.selinux=
Or default.prop by utilising ro.boot.selinux=
Or via devices init.${ro.hardware}.rc
on early-init
# Set the default standard for our SELinux mode
setenforce 0
Or
setenforce 1
If you want to do it in OS then if custom rom go to dev options enable terminal and root access to shell (adb)
Open terminal and use the commands below
su
setenforce 0 or 1
If you want to try and use an app for changing selinux then you can try selinux changer app
Hope this helps