In 'walk slowly', the adverb 'slowly' modifies the verb 'walk'.

在walk slowly中，副词slowly修饰动词walk。

《牛津词典》

Mr. Craven got up and began to walk slowly across the room.

克雷文先生站起来，在房间里缓缓踱步。

youdao

He takes one and we walk slowly down thecorridor.

他拿了一块，我们慢慢地沿着走廊网下走。

youdao

They are known for their ability to walk slowly and safely on the paths.

VOA: special.2009.10.07

Adults and children can be seen testing it as they walk slowly in and out of the thick haze.

BBC: Look on the bright side at London��s light show

Soon I flub a shot, and my son encourages me to take it easy: "Just walk slowly and clear your head, " he says.

WSJ: How Mom Plays the Game | Golf Journal

Surprisingly, after three months of therapy 90% of those with some sensation and movement recovered the ability to walk slowly, no matter which type of training they had gotten.

FORBES: Magazine Article