Hair dye!!!

I recently dyed my hair guyz!! but unfortunately when trying to get all the dye out i used to much hot water to help and afterwards the dye looked fine but i just started coming out afterwards ;-; BUTTTTT im gonna re dye with manic panic!! i would not recommend using splat it does wash out fast and stains EVERYTHING!! also i know that you use cold water to wash your hair but how do you get the dye out when you first wash it without having to use hot because that’s what i was struggling on since this was my first time dying my whole head blue!! any tips would be very appreciated thank you!!!! okii that’s all baibai!! ^-^