I am looking at this part of the documentation API · QuantumOptics.jl
You already have a correct tspan and rho0.
You need an f function for your third argument that returns a tuple (H, J, Jdagger) where H is the hamiltonian at time t and J is the list of collapse operators at that time. I guess the lists J and Jdagger will be empty in your case.
Maybe you have been looking at the other part of the documentation:
This is referring to a particular way to represent time-dependent operators much more efficiently and “lazily”. E.g. like this one API · QuantumOptics.jl
These are quite a bit more advanced. Happy to discuss them as they are a pretty interesting piece of functionality, but I think it would be better to first have the simpler implementation from above done, so that we have a good starting point.