The pronunciation of regular verbs in the past or in the past participle that end in ED can be tricky and difficult to do. English pronunciation seems like it has few rules and there are of course many irregularities, but there are many ways of knowing how to pronounce words that you have never heard before.
The best way of knowing how to pronounce words that end in ED is to focus on the last letter of the stem of the word. For example, Work = the final sound is K or decide = the final sound is D. All you need to do is use this list as a reference to know how to pronounce the ED ending.
You need to remember that pronunciation is a physical process and you must practice with repetition, as cited HERE. The best way to practice is to start with the sound /K-T/, then repeat a word like “Worked” and then a sentence, for example. My Granddad worked in a bank.
When we pronounce the …ed endings, there are 3 sounds /id/ /t/ /d/:
/id/ is when the verb ends in D or T
/t/ is when the verb ends in CH, F, GH, K, P, S, SH, X
/d/ is when the verb ends in AY, B, G, L, M, N, OW, R, V, Z
We never pronounce it /ed/. Be careful!