Whispering gallery mode (WGM) microresonators emerged as a promising platform for highly sensitive sensing applications due to their high-quality factors and small mode volumes. They offer the advantages of the ultrahigh sensitivity and compact size, rendering them suitable across multiple fields. A stable encapsulation process is essential for practical applications to establish a reliable coupling system between the microcavity and its waveguide coupler, especially for the microtoroidal resonator and tapered fiber coupler. However, adjusting the coupling coefficient after the packaging process poses challenges, thereby compromising coupling accuracy and limiting its range of applications. It is imperative to provide a platform of tunable coupling for packaged WGM resonators. Here, we provide an approach for leveraging the magnetostrictive effect to dynamically regulate the fiber-cavity coupling, enabling the measurement of the magnetic field as an example. Moreover, we show the fine-tuning of coupling within the packaged WGM microresonator, allowing the precision control of the optomechanical effect. Through this method, a tunable coupling platform in a packaged system is realized, opening up new dimensions of research in various fields.