My speech language pathologist said words like ‘chicken’ are typically harder to say because it starts with a ‘hard’ sound. She said the way through it, for me, is to try gentle onsets. Which is basically expelling air before you say the word to prevent a block. So…’chicken friend chicken’ becomes ‘hhhhicken fried hhhicken’. Eventually you can lessen that gentle onset to speak more normally. It worked for me, but it was awkward for a long time. It’s best to practice a lot by yourself first