I'm struggling to perfect my French accent - how can I improve this quickly and independently?

Media! Films, songs, TV shows - anything which exposes you to the language while keeping you interested is a good way to work on your accent without even realising you're doing work. Personally, I love musicals, so for the past few years I've been really invested in the French musical theatre scene and have learnt so much via the scripts and songs. Many French musicals are available in full on youtube if you want to investigate. My favourites are Mozart l'Opéra Rock and Robin des Bois :)
Other French singers/musicians I recommend checking out: Kendji Girac, Soprano, Stromae, Joyce Jonathan, Maitre Gims