How to reduce separation anxiety?

I have the next month off of work and have committed this time to get a good start on training my bichon puppy. Going great so far in the first month other than separation anxiety - I cannot leave the room without him barking. I’ve left the house while recording her and it appears she even barks when nobody is home. I live alone in an apartment complex with neighbors nearby so this cannot continue. I’m willing to try anything in order to avoid rehoming her if anyone has tips. Thanks in advance.