To practice speaking, a couple of classes with teachers specializing in OET preparation are enough. You can find teachers on various services, read more about it here https://godsempires.com/why-oet-result-is-delayed-l-en/.
The situation with the letter is more complicated. The structure of writing on the OET exam has its own characteristics, and examples can also be found on the official website. In addition, there are free videos on YouTube about preparing for a letter from the E2 service, and their paid videos will be included in the basic package when using the company’s services. Also, for the proper development of writing skills, I strongly recommend using the Swoosh service — a set that includes checking 8 of your letters by real teachers, as well as 5 additional trial exams.
To get an ECFMG certificate, you need to score at least 350 points for each section. If at least one part of the exam falls below the set minimum, you will have to retake it completely. At the same time, the number of attempts is unlimited, since ECFMG sees only the exam attempt that you open access to yourself. You need to register for the exam on the appropriate website, where you select the country and the date of its completion.