At one point I held a mechanic's certificate. However due to poor judgement it(the certificate) was revoked due to a narcotics conviction.
How can I get it reinstated? Is there refresher classes?
I think you've to apply for a certificate again after the required period and take the tests again. From 14 CFR §65.11 Application and issue:
(d) Unless the order of revocation provides otherwise—
(2) A person whose mechanic or repairman certificate is revoked may not apply for either of those kinds of certificates for 1 year after the date of revocation.
In your case, you have to wait for 1 year after the final conviction to apply. From 14 CFR §65.12 Offenses involving alcohol or drugs:
(a) A conviction for the violation of any Federal or state statute relating to the growing, processing, manufacture, sale, disposition, possession, transportation, or importation of narcotic drugs, marihuana, or depressant or stimulant drugs or substances is grounds for—
(1) Denial of an application for any certificate or rating issued under this part for a period of up to 1 year after the date of final conviction;
In addition to the articles listed above, you must first seek out an Approved (SAP) substance abuse professional to administer “treatment/punishment” then submit to supervised drug screens for a determined period of time thereafter, which is decided based on individual case stipulations and risk factors of repeated offenses until the time period determined has expired then you may reapply and retake all tests including oral and practical examinations in addition to the three written. Plus you may have to pay additional fees and penalties for the infraction in addition to the fees for the tests and the test administrators.