How to run mediation analysis in SPSS with three conditions (1 control and 2 treatments)

Question

I have three conditions in my experimental design

1. Control (No treatment at all)
2. Treatment Level 1
3. Treatment Level 2

My hypothesis is that treatment Level 2 will increase DV better than the others (control and treatment level 1 could yield similar outcome).

Also, I have found in my pilot study that IV increases DV via serial mediators (M1, M2) as full mediation. (Pilot study has 1 control and 1 treatment)

If I want to do mediation analysis for these three conditions, how should I do? How should I code my data and which model I should use?

Really appreciate your help!

I tried using several Hayes's model but the moderated mediation ones did not work. Meanwhile, I tried coding the three conditions to three level and use model 6. It works but I'm not sure whether its right or wrong.