My ds had a speech delay - maybe not quite as severe but really got very muddled (limited vocab, words coming out in wrong order, missing or “swallowing” first syllable or consonant sound of many words, couldn’t cope with tenses etc)
I couldn’t get anyone to help me so I tackled myself.
lots of singing and rhyming if possible - my dc resisted but we found songs he likes eg Yellow Submarine and Bob the Builder
keep your own speech very simple and make sure you maintain eye contact when you converse. Sometimes, when dc is not tired, ask dc to concentrate on what you are saying carefully and repeat what you have said. Or when you ask a question ask dc to try again when you don’t understand the reply. It is okay to smile and say to dc “I think I understood but please could you try saying that again and really think about your words.”
then repeat back to dc very slowly what is the correct pronunciation and grammar
tbh this didn’t really help with ds but it is recommended and can’t hurt.
Focus on one or two words or sounds for a few weeks - ask dc to look at your mouth while you say the word , get dc to then say it along with you, then ask dc to try alone. If that is hopeless just make the shape of the sound quite exaggerated so you show him how to get mouth in the right shape and see if he can copy. Keep it relaxed.
Remember certain sounds are often very late to arrive - dc still struggles with “th” and “y” (age 6.5). You can get a list of sounds that kids struggle with online so you know which ones really aren’t worth pushing yet.
regarding reading: I found it was absolutely unrelated to speech with ds, really weird! He learned the letters and he can read
well now. Sometimes sounding out words phonetically helps! As it actually reinforces what a word sounds like and also breaks bad habits eg my ds always said “acause” “afore” instead of because and before. That gets fixed when you read!
don’t lose hope