Using below input file (H2CO.gjf) to carry out a excited state calculation by Gaussian via TDDFT (note that the "root" option is default to 1).

# B3LYP/def2SVP TD density pop=MK IOp(6/33=2,6/42=6)

test

0 1
 C                  0.00000000    0.00000000    0.52887991
 H                  0.00000000    0.93775230    1.12379107
 O                  0.00000000    0.00000000   -0.67757652
 H                  0.00000000   -0.93775230    1.12379107

Boot up Multiwfn and input below commands:

H2CO.gjf
7  // Population analysis
18   // RESP module
8  // Will load ESP fitting points and ESP values from Gaussian output file
1  // Standard two-steps RESP fitting
H2CO.out   // The Gaussian output file
Now the RESP charge for S1 state of H2CO is obtained, as shown below.

   Center      Charge
     1(C )   -0.322094
     2(H )    0.196640
     3(O )   -0.071185
     4(H )    0.196640
 Sum of charges:    0.000000
 RMSE:    0.004375   RRMSE:    0.344520

If RESP charge for e.g. S3 is needed, use "TD(nstates=5,root=2)" instead of TD in Gaussian input file.