if you dont want to get lessons yet, you might could use some online videos for a bit, this is what i do. the person in my source makes good vids and can communicate well. he covers a few videos about slicing among many others

though, im a lefty as well, are you sure its not a hook? for lefties, a slice is when it heads left and vice verse

And the best news of all… there is a golf swing guide out there that can eliminate your slice, and change your life… allowing you to feel satisfied and fulfilled after a round of golf!

Do you play Baseball or Softball?
If so, you are dragging you back shoulder through impact.
If you don’t play Baseball, take a look at your hand position when you grip the club.
Are you seeing the knuckles of your gloved hand?
If not, try gripping the club and have the “V” that is made between your thumb and fore finger point to your left shoulder, this is called a weak grip.
Just remember where your sweet spot is when you practice, so you can take it to the course.
Also, just prior to hitting your drive after you set up, raise the club to shoulder height and take a few swings that way, then tap the ground with the head and then take your swing.

Good luck and have fun.

you need to have a coach to get the straight hit.it is basically about the balance.

A good drill to fix a slice is to go to the range with a bucket of balls, tee up each shot, make sure you release your wrist at impact, do this with about 10 balls or go then try hitting a couple of full shots, this should help.

Have a good one…

Refer to this earlier reply to the same question:

Regards.

Hi,
You could look at the videos here.
Good luck.

Yes. I used to slice the ball after my tee shot with driver. After follow the instruction from my local Pro and practice to swing from inside out then my tee shot now is straight (80%) or hock (20%) which give me more distance.
I recommend you to learn from the link below: How to solve your slice problem?