MIXAMO animation slow down walk cycle

Hello, I ask for your help because I am new to Blender, I have a walk cycle mixamo animation and I would like to slow down the walk at the end of the course without using NLA because I use the Animation_Layers plugin which does not allow the use of the NLA. The problem is that if I scale on the timeline the keys (S) for example value 2, the transition is too brutal and is not smooth. Thanks for your help !