A solution of iodine antiseptic is a medical item that is used for improving health. There are two ways to treat your cracked cap.
#1. If you inspected the bottle in the drug store before you bought it, you would not buy this bottle. Almost all over-the-counter medicines have warnings: Do not use if the safety seal is broken. So, out of utmost caution, do not use this iodine, because it might be contaminated (even tho you are the only one who could have contaminated it). Look at it this way: you bought a bottle of iodine solution, you had its potential usefulness for a year to keep your skin abrasions antiseptic (even tho you did not have the need to use it). It can be considered to have served its purpose usefully; get a new bottle and be more careful.
#2. Being the cheapskate that I am, I would examine the bottle: has the liquid level dropped and dried out? Is it gooey so as to be difficult to apply? If not, it might be OK to keep and use. On the other hand, a cracked lid is an invitation to disaster - if the bottle gets knocked, it will leak - probably onto the item you just laid down, which will, of course, be very important and/or delicate. To avoid catastrophes of this sort, dispose of the iodine solution. You will feel more secure. Get a new bottle.
Or, get a tube of antiseptic ointment, which will have less tendency to spill, unless you step on it.