Need help to create an update query mysql

I am working on upwork type project and want to create an update query for bids.

User have free bids(which he get by default per month) and pro bids which he can buy for certain amount.

Now if he would apply on any job then I want to update -1 for job_quota(if it is not 0 already), then -1 from pro bids in ascending order.

My table structure(in user table):

users

job_quota -------->id

12---------------->53

Buy_bids

id---->no_bids--->amount_paid--->user_id 

1-----> 20------------>20---------------> 53

2-----> 20------------>20---------------> 53

3-----> 20------------>20---------------> 53

I have an idea like this, but I do not how to implement it into mysql query:

$query=<<< SQL
update users set job_quota=job_quota-1 if ( job_quota !=0 )
else update buy_bids set no_bids =no_bids-1 where user_id=53
SQL;

Can anyone suggest me how can I achieve it, I am not looking for accurate solution but I need your help and suggestion what should I try to achieve this.

Many Thanks.

Answer:

This is my proposal:

UPDATE users
    IF (job_quota NOT IN 0 )
    THEN  SET job_quota = -1
    ELSE (UPDATE buy_bids SET no_bids = no_bids -1 
          WHERE users.id = 53)
WHERE id= 53