This one is simple. All you need is a stopwatch, and the clock app on your phone is the fastest option.
Start by choosing a sentence or a short passage in English that you want to say fluently. Around three sentences is the sweet spot. If you want to work on something longer, drill the short sentences first and assemble the passage afterwards.
Then do this. Time yourself saying it. Now try to say it faster than you just did. Repeat three times, or as many as you like. More is better.
When you cannot beat your previous time any more, work out what is holding you up. Usually it is a hesitation on particular words or phrases. Drill those in isolation a few times, then go back to the whole passage.
Done this way, you find the exact words and phrases that are breaking your fluency. Fix those and the smoothness follows.
If the problem is mispronunciation instead
Use the same method in reverse. Rather than going faster and faster, say it as slowly as you possibly can. When you cannot go any slower, pick out a few words and pronounce them very slowly and clearly to force yourself down. Repeat until you are happy with how it sounds.