“以拇指拨弄”可以翻译为 “fiddle with (something) with one's thumb” 或者更简洁地表达为 “thumb through/at (something)” （不过“thumb through”更多有“匆匆翻阅”之意，若单纯强调拨弄动作，“fiddle with...with one's thumb” 更贴切），但最直接对应且强调用拇指拨弄这一动作的常见表达是 “fiddle with something using one's thumb” 或简化为 “fiddle with something with the thumb” （“fiddle with” 本身就有“摆弄、拨弄”的意思）。
例句：
He was fiddling with his pen with his thumb, looking a bit nervous.（他正用拇指拨弄着他的笔，看起来有点紧张。）