How to enable disable PLL clock in ARM cortex M4

Hiii
i have use ARM cortex M4(M453VE6AE) I want logic /code about to PLL disable & enable.
1) how to reduce current below 1mA without applying power down mode .
2) How to disable PLL clock & enable HIRC clock after that function(in this function one condition is check and hold for 5sec counter) is execute after that disable HIRC clock and enable PLL clock