I believe this is a situation that can be explained to the judge but any changes in treatment agencies must be reported to the court. You are better off with a lawyer because a lawyer will best explain what happened and what you have done.
Yes, you may be ok if you bring proof of the new treatment and letters showing clean UAs and treatment compliance and make sure the court/ probation is aware that you are still in treatment. If you explain what happened to the judge, you should hopefully be ok. It will be easier to have an attorney represent you, but you could always take your chances without one, or see if you can get public defender for it.
If you can afford a lawyer, it's always helpful to retain one. If you can't, you can probably handle this by explaining the situation and showing that you took immediate and proactive steps to remain in compliance. Missing a UA with a legitimate reason is better than having a dirty UA.
It's unclear how long ago this happened - if only a few days ago, and depending on the circumstances, an attorney experienced in DUI defense might suggest you obtain an ETG test through a state certified agency. ETG testing can screen for alcohol consumption up to 96 hours before the test; a clean ETG taken within a day or two of the UA you missed will help show that you didn't miss it because you knew you had something to hide. Your account, however, sounds as though more time than that has passed so an ETG may not help you. The fact that you're back in treatment, however, along with a clean UA does.
As everyone else on here has already said, however, you should consult with an attorney as soon as possible. If you had an attorney earlier in the case, consult them (if feasible) - if you had a public defender, contact the agency that provides that service to your court. Being proactive is more than half the battle with review hearings. Good luck.
Mr. Kertchen's analysis is very good; you should try to retain a lawyer if you possibly can. The lawyer may know the probation officer or judge that is involved. You should not try to leave your situation to chance or good luck. However, if you simply can not afford to retain a lawyer, you may well be able to be represented by a public defender at no cost. You must contact the particular court to learn how to be put in contact with the public defender agency representing that particylar court system. Good luck.