How can I arrange the GAMS code in order to do the following step?

1. Solve MIP problem

2. Fix binaries to the values obtained in 1.

3. Solve LP problem

With the binary variable alfa, I tried this

*solve Model using MIP minimizing z;*

loop ((k,time),

alfa.fx(k,time)=alfa.l(k,time) ;

);

solve Model using LP minimizing z;

loop ((k,time),

alfa.fx(k,time)=alfa.l(k,time) ;

);

solve Model using LP minimizing z;

but it doesn't work and I obtained the following error:

*equation potenza.. discrete variable "alfa" not allowed*

How can I fix the binary variable to the values obtained and use it as a parameter? (changing the name in all equations would take considerable time)

Thank you in advance