Self soothing

How can I help my baby learn to self soothe? She’s just turned 4 months and I’ve just got her to 4 naps from 5. She wakes at 8am and sleeps at 7pm.

Her first wake window is usually 1.5hrs. But as her nap times vary (usually 30-40mins unless she happens to do a random 1hr nap which is usually if I give her a bath etc) I’ve been having to do her last nap as a contact nap just to help her so she isn’t over tired before bed and can also have a semi decent wake window before bed. Stretching her to 2 hours can probably work once in the day if she has a decent 1hr nap but that’s honestly so rare as I feel like she’s having trouble connecting her sleep cycles. Her average wake window id say is 1.75. The shortest being 1.5 in the morning and evening before bed and longest being 2 (as mentioned above 2 is rare).

She takes a dummy and I also use white noise for her naps/sleep and keep the room dark.

How can I help her soothe herself to sleep. The dummy helps but if it drops out or she’s too tired, she requires my help either by rocking her bassinet or I have to pick her up and rock her to sleep and then transfer her back to the bassinet.

I’m open to trying anything. I just want to help her connect her cycles as it’s so obvious after her 30minute naps that she’s still tired and could’ve done with a much longer nap. This also plays into the rest of the day and this is where I struggle to extend the rest of her wake windows.

The nights are not too bad. She’s going through a regression so going to sleep has been hard for her and then she has also been waking up very often but she’s able to put herself to sleep if I give her the dummy or once she’s had her night feed. Some nights are worse than others but she’s definitely better at night than she is during the day.

Please help! Do I work on naps or the nights first? What do I do to help her connect those cycles and also go to sleep herself ? Is she too young to start this?? Will she do this herself??