When to Reapply
Applicants often wonder if it is advisable to reapply for a job which they have already applied for in the past. The short answer is that if you find the position to be very attractive, there is usually nothing to lose other than your time. Your chances of receiving serious consideration the second time around will be greater if considerable time has passed and/or if you have enhanced your credentials in some way.
Many employers don't bother sending rejection letters, so you may not even know that you were rejected. The applicant pool may have changed since you first applied and you may have a better chance of getting selected this time.
If you made the interview stage previously and were a finalist or received positive feedback then you may be a strong enough candidate to receive an offer this time since there might be a less competitive pool.
Another reason to consider reapplying if time has passed is that the staff responsible for screening resumes may have changed and the new screener(s) may have a different take on the viability of your credentials. Typically it doesn't make sense to reapply until at least four months have passed since your initial application.
What to Write in Your Cover Letter
Typically, you would refer to your prior application in your cover letter if you have previously interviewed for the position. You can mention why you were convinced that the employer and the job were an excellent fit as a result of that exposure.
If you didn't receive a rejection letter or weren't interviewed and considerable time has passed, you would have the option of omitting reference to your previous application in your letter.
Target Your Resume and Letters
Most large, and many smaller, employers use talent management systems to screen applicants. Take the time to target your resume and your cover letter, including keywords that match the job posting, so you will have a better chance of getting your application considered for the job.
Be sure to highlight in your cover letter any additional experiences, awards, accomplishments or training which you have amassed since your last application.