Where to put 从头到尾 in a sentence?
1.我 [从头到尾] 把他的电影看了一遍。


2.我把他的电影 [从头到尾] 看了一遍。

Both are idiomatic.
[从头到尾] is an adverbial phrase that can be placed before or after the object [他的电影]. Just like the two sentences above.
In either case, the adverbial phrase must be placed before the verb phrase [看了一遍]
#1 place the adverbial phrase before the object. It emphasizes the adverbial phrase [从头到尾](from start to finish) -- What do you do from start to finish?
#2 place the object before the adverbial phrase. It emphasizes the object [他的电影] (his movies) -- What do you do to his movies?